This project seeks to determine how waking neurobehavioral functions (sleep propensity, cognitive performance, sleepiness, and mood) are affected by partial sleep deprivation (PSD). PSD has been identified as a serious public health problem being experienced daily by millions of people as a result of medical, psychiatric, and sleep disorders, as well as social demands (work, family, travel). Although highly prevalent, little scientific work has been done on the nightly duration of sleep and number of days of PSD that will lead to daytime sleepiness, involuntary sleep episodes, performance failures-- information that is essential to determining the level of PSD that could result n accidents (e.g., motor vehicle). In a preliminary study, we developed a protocol for studying PSD and demonstrated the sensitivity of a set of neurobehavioral measures to sleep restriction over 1 week. Utilizing this approach, a randomized control trial using independent groups was initiated to test the effecs on waking function of the types of sleep restriction most commonly experienced by people. The purpose of this study is to determine the nature of the cumulative waking changes in neurobehavioral functions engendered by restricting nocturnal sleep to 4.0 hrs, 6.0 hrs, and 8.0 hrs (control) per night for 14 consecutive nights, when the sleep is placed at different circadian phases. Following a 7-14 day period at home, during which time the subjects are monitored to ensure they have a stable sleep/wake cycle, subjects will live in the Inpatient Study Unit of the CRC for 20 consecutive days, during which time their sleep and waking neurobehavioral functions are monitored. Following 3 baseline days of 8-10 hr sleep/night, subjects will be randomly assigned to one of the three sleep restriction conditions (4,6,8 hr/night) for the next 14 days, followed by 3 days of recovery sleep (8 hr/night). Changes in sleep polysomnograpy and waking neurobehavioral functions at different circadian phases across the 2-week period of sleep restriction are compared among the three groups.